Feline Immunodeficiency Virus

by Holly Frisby, DVM

What is feline immunodeficiency virus?

Feline immunodeficiency virus (FIV) is a type of virus called a retrovirus. It is in the same family as feline leukemia virus (FeLV) and human immunodeficiency virus (HIV, the virus that causes AIDS). It attacks the immune system, and as a result, the cat is unable to fight off various infections and cancers.

There is no evidence FIV can be transmitted to mammals other than cats.

Retroviruses are species-specific. This means a feline retrovirus like FIV will only infect cats; a human retrovirus such as HIV will only infect humans.

Retroviruses are made up of RNA. In the host, the RNA is transcribed into DNA and incorporated into the DNA of the host’s cells.

Retroviruses are fragile, being easily inactivated by ultraviolet light, heat, detergents and drying.

How is FIV transmitted?

FIV is NOT transmitted by prolonged close contact, as is the case for FeLV. FIV is shed in the saliva and is transmitted by bite wounds.

FIV transmission in utero or through the milk is very rare. It can occur if the queen is infected during gestation or lactation. Queens infected with FIV prior to the pregnancy usually have noninfected kittens.

How common is FIV?

FIV is found worldwide in domestic cats, and also infects wild felines including snow leopards, lions, tigers, jaguars, Florida panthers and bobcats. Although the virus was first isolated in 1987, we know the virus has existed for many years. It is most common in outdoor, free-roaming cats. In the United States, 1-8% of apparently healthy cats are infected with FIV.

Male cats are twice as likely to become infected with FIV as female cats. Free-roaming cats are also more likely to be infected since they too are more susceptible to bite wounds. Unlike FeLV, FIV infection is rare in catteries since few bite wounds would be expected in a cattery situation.

How does the virus cause disease?

FIV infection in cats has three stages, just like HIV infection in humans. The initial or acute stage of FIV infection is often characterized by fever, swollen lymph nodes and a susceptibility to skin or intestinal infections. This stage generally occurs 4-6 weeks after being exposed to the virus.

The second stage is a latent or subclinical stage in which we see no signs of disease. This stage can last for many years. During this stage, the immune system may slowly be destroyed. When the immunodeficiency becomes severe, the third stage of infection occurs.

The third stage is the final or AIDS-like stage, and occurs most commonly in cats 5-12 years of age. (FeLV is seen most often in cats 1-5 years of age). During this final, clinical stage, the cat's immune system is not functioning correctly since the virus kills essential cells in the system. Because of this, the cat is very prone to infections. These infections, which are usually chronic, may be bacterial, fungal or parasitic. Often they are caused by organisms which normally do not cause severe disease in cats. But since the immune system cannot keep them in check, they multiply rapidly and cause disease. These are called opportunistic infections.

We can see chronic upper respiratory tract infections, intestinal infections, and skin/ear diseases. Certain cancers may develop in some cats; researchers are determining how FIV is involved. Other cats may show neurologic signs although FIV generally has less effect on the nervous system of cats when compared to the effect of HIV in humans. Anemia can occur and may be a result of a parasitic infection. Once a cat is in the late stages of disease, life expectancy is 1 year or less.

What are the clinical signs of disease?

FIV-infected cats may show nonspecific signs such as lethargy, loss of appetite, fever, swollen lymph nodes (lymphadenopathy) and weight loss. The signs of FIV infection and FeLV infection are very similar.

Chronic oral infections occur in approximately 50% of cats with FIV-related disease.

Oral Infections: Chronic oral infections occur in approximately 50% of cats with FIV-related disease. Cats may show pain when touched on the face, have difficulty eating or refuse to eat, and may have a bad odor around the mouth. These infections can be difficult to control. Oral infections are more common in cats with FIV infection than those infected with FeLV.

Respiratory Disease: Approximately 30% of FIV-infected cats have chronic upper respiratory disease with sneezing and nasal discharge. These symptoms may be due to chronic infections with feline herpes (rhinotracheitis) or calicivirus. In some cats, pneumonia can develop and cause coughing and difficulty breathing.

Eye Disease: Along with signs of upper respiratory disease, cats may also show ocular signs such as redness of the eyes, discharge and cloudiness of the cornea. Glaucoma is sometimes seen, as well.

Gastrointestinal Disease: Chronic diarrhea is seen in 10-20% of FIV-infected cats. It may be due to cancer, bacterial infection, parasitic infestation or FIV itself.

Skin and Ear Infections: Recurrent or chronic infections of the skin and ears may be the first sign of an FIV infection. Because of the immunodeficiency, parasites, yeast and bacteria overgrow and cause symptoms such as hair loss, itching, and pustules. Demodectic and notoedric mange, which are unusual in healthy cats may be seen. Chronic ear mite infections and aggressive ringworm lesions have also been reported. Chronic abscesses can also occur.

Neurologic Disease: Changes in behavior, loss of house-training, and dementia can be seen in FIV-infected cats. These symptoms may be caused directly by FIV or by parasitic (Toxoplasmosis) and fungal (Cryptococcosis) infections which occur more often in immunosuppressed animals.

Lymphadenopathy: Lymph nodes in the abdomen and other parts of the body are often enlarged.

Anemia: Anemia is observed in approximately 1/3 of FIV-infected cats. Haemobartonella felis, a parasite of red blood cells, may be responsible for many of these cases.

Neoplasia: FIV-infected cats are 5 times more likely to develop lymphoma and leukemia than uninfected cats. The exact mechanism for this is unknown.

What are the laboratory findings in cats with FIV-related disease?

Most chemistry tests are normal in cats with FIV. We may see anemia and decreased numbers of white blood cells in ill cats. A certain protein, called globulin, may be elevated in FIV-infected cats.

How is FIV infection diagnosed?

FIV infection is diagnosed through tests which detect the cat's antibodies against FIV. Antibodies are usually present 3-6 weeks after infection. In Spring 2001, The American Association of Feline Practitioners (AAFP) revised their guidelines for FIV testing, and made the following recommendations:

  FIV FeLV
During Sickness When cats are sick, regardless of previous negative results. While many signs (such as fever, stomatitis, vomiting and diarrhea) are obvious indicators of illness, other signs are subtle and may include changes in behavior, grooming and eating habits. Same as FIV, including sick cats that have been vaccinated for FeLV.
New Adoptions When cats and kittens (regardless of age) are newly adopted, whether or not they will be entering a household with other cats. Same as FIV.
Multi-cat Households When cats live in households with unknown FIV infection status. Infected cats can remain asymptomatic for years, during which time they may transmit the virus to uninfected cats. Same as FIV when cats live in households with unknown FeLV status.
After Potential Exposures When cats have had potential exposure, such as a bite inflicted by a cat of unknown infection status. Such cats should be tested a minimum of 60 days post-exposure. When cats have had known or possible exposure to other cats of unknown infection status (e.g., cats that go outdoors unsupervised). Periodic testing may be justifiable in cats at continued risk of exposure even though adults are relatively resistant to FeLV infection.
Routine Testing Annually, when cats at high risk of infection. Cats are at high risk of infection include those that fight or those that live with FIV infected cats. No recommendation at this time.

In addition, is is important to note that:

  • FIV tests detect antibodies (FeLV tests detect antigens). All positive screening tests (the "ELISA" is preferred) should be confirmed through a test called the Western blot. Remember, though, no test is 100% accurate.
  • It takes at least 8 to 12 weeks after infection for detectable levels of antibody to appear. Therefore, cats should be retested about 8 to 12 weeks after their most recent exposure in order to allow adequate time for development of antibodies. Cats with an unknown infection status should be tested once, then have the test repeated in 8 to 12 weeks.
  • Young kittens may have positive test results for 12 to 16 weeks after birth because of the passive transfer of FIV antibodies from the mother. Only a small percentage of these kittens who test positive are actually infected. A postive test result in an uninfected kitten is called a 'false positive'. Conversely, an infected kitten may have a falsely negative test if it has not yet had time to develop antibodies. Kittens tested at less than 6 months of age, regardless of the test result, should be retested after 6 months of age.
  • Remember that FIV-infected cats, unlike FeLV-infected cats can live for many years before they develop symptoms.

To assist your veterinarian in determining the risk of your cat being exposed to FIV, the AAFP has developed an Observation Form you can fill out and give to your veterinarian at your cat's next exam. Click here to see a sample form.

How is FIV infection treated?

To provide the best care, your veterinarian needs to know if your cat is FIV-infected.

Although FIV-positive cats can live for many years, your veterinarian needs to know if your cat is FIV-infected to provide the best care e.g., proper vaccinations and aggressive treatment of infections. Stress and exposure to ill animals should be avoided. FIV positive cats should be kept indoors both to protect them from exposure to disease and also to prevent them from spreading FIV to other cats.

There are many antiviral medications for people with HIV infection, but currently there are none which are routinely and effectively used in FIV-infected cats. Some drugs that directly affect the immune system have been used with variable but encouraging results. These include Propionibacterium acnes (ImmunoRegulin), low doses of oral human alpha interferon and an aloe derivative called Acemannan.

Cats with FIV-related disease will need to be treated according to the signs of disease they are showing. Infections which occur as a result of the immunodeficiency should be treated aggressively. FIV-infected cats with cancer can receive chemotherapy, radiation therapy or immunotherapy. Supportive care such as fluids, good nutrition, and antibiotics for secondary infections are essential.

How is FIV infection prevented and controlled?

Testing and identifying positive cats is the only means by which FIV infection can be controlled. Although FIV is less transmissible than FeLV, any FIV-positive cat should be separated from non-infected cats. Cats in the terminal stages of the disease can shed large amounts of the virus in their saliva and can pose a greater threat to uninfected cats.

Since cats who roam are more likely to sustain cat bites, cats should be kept inside, or supervised when outside and not be allowed to roam.

There is no FIV vaccine available.

Are there human health risks associated with FIV-infected cats?

The retroviruses are species-specific. There is no evidence FIV can be transmitted to mammals other than cats. A potential human health risk can occur from exposure to some of the secondary infections FIV-infected cats may acquire, such as toxoplasmosis.

References

American Association of Feline Practitioners/Academy of Feline Medicine. Recommendations for Feline Immunodeficiency Virus Testing. The Compendium on Continuing Education for the Practicing Veterinarian. 1997:1105-7.

August, JR. Preventive Health Care and Disease Control. In Sherding, RG (ed). The Cat: Diseases and Clinical Management. Churchille Livingstone. New York, NY; 1194;524.

Barr, MC; Olsen, CW; Scott, FW. Feline viral diseases. In Ettinger, SJ; Feldman EC (eds): Textbook of Veterinary Medicine. WB Saunders Co. Philadelphia, PA; 1995;409-435.

Barr, MC. Feline immunodeficiency virus. In Tilley, LP; Smith, FWK (eds.) The 5 Minute Veterinary Consult. Williams and Wilkins. Baltimore, MD; 1997;584-5.

Bell, FW. Recommendations for FeLV- and FIV-positive cats with cancer. In August, JR (ed) Consultations in Feline Internal Medicine. WB Saunders Co. Philadelphia, PA; 1997:572-8.

Dow, DW; Hoover, EA. Central nervous system infection with feline immunodeficiency virus. In August, JR (ed) Consultations in Feline Internal Medicine. WB Saunders Co. Philadelphia, PA; 1997:403-405

English, RV. Feline immunodeficiency virus. In Bonagura, JD (ed). Current Veterinary Therapy XII. WB Saunders Co. Philadelphia, PA; 1992;280-286.

Hopper, CD; Sparkes, AH; Harbour, DA. Feline Immunodeficiency Virus. In Chandler, EA; Gaskell, CJ; Gaskell, RM (eds).Feline Medicine and Therapeutics. Blackwell Scientific Publications. Cambridge, MA; 1994;506-514.

Sherding, RG. Feline immunodeficiency virus. In Birchard, SJ; Sherding, RG (eds): Saunders Manual of Small Animal Practice. WB Saunders Co. Philadelphia, PA; 1994;91-3.

Squires, RA. Pathogenesis, prevention and treatment of feline retroviral infections. Presented at the 79th Annual Convention of the Wisconsin Veterinary Medical Association. Madison, WI; October 16,1994.

Zenger, E; Wolf, AM. An update on feline retrovirus infections. In Kirk, RW; Bonagura, JD (eds) Current Veterinary Therapy XI. WB Saunders Co. Philadelphia, PA; 1992;272-277.

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